var a=10; //声明变量a
console.log(a);//控制台输出日志

// 书写代码顺序
console.log(b);
var b='hello';
//解析代码顺序
var b;
console.log(b);//undefined
b='hello';





var c =10;
var c='hello';//string
var c=true;
console.log(c);


